I just discovered the answer to this problem.
I’m using a KORG MicroSAMPLER as a midi controller, and found that I couldn’t get to the bass notes I needed, no octave options on the unit - it CAN be used as a midi controller but isn’t the best option for this purpose.
I’m also still running Cubase 6 so things might have changed in the newer versions, but:
Select your track - the options/headings on the left, under the heading ‘MIDI Modifiers’ there is a ‘Transpose’ option - slide this up or down in increments of 1 to transpose your MIDI input up or down semitones.
Hands-down, this is what OP was asking for